Plunger drive for pumps



June 5, 1945. w. HUBER 2,377,554

PLUNGER DRIVE- FOR PUMPS Filed Dec; 17, 1943 Zmnentof (Ittornegs reamed i s, 1945 PLUNGER DRIVE FOR PUMPS Matthew W. Huber, Water-town, N. Y., assignor to The New York Air Br ration of'Ncw Jersey ake Company, a dorm- Application December 17, 1943, Serial No. 514,688

- Claims. (01. 74-56) This invention relatesto pumps of the parallel cylinder type in which the plungers are actuated by a swash plate, and the novelty resides in the plunger actuating mechanism.

In prior applications Ser. No. 462,563 filed October 19, 1942, and Ser. No. 506,091 filed October 13, 1943, there are described pumps of the type named, in which the plungers are biased toward the swash plate by coil compression springs, each of which encircles its plunger and reacts against a flange encircling the plungerhead. 3

In some'installations for which the pump is suited, the pump revolved in an.orbit at high speed, the axis of the pump being parallel with the axis about which the pump revolves. This develops large centrifugal forces which act transversely to the plungers and deflect the mid portions of the springs into rubbing contact with. the plungers. The springs are ultimately damaged by wear, and have been known to fail in consequence.

The present invention provides a spring so short that it cannot be so deflected. Further the spring merely takes up back-lash or clearance and is not worked by the operation of the pump. Consequently the problems of spring-design and manufacture are greatly simplified.

The invention can be used in any parallel cylinder pump to avoid the use of return springs characteristic of the earlier applications, but is'believed to be advantageous chiefly in those cases where the space available or some other consideration limits the length of the spring to a value such that the plunger stroke is unduly large in proportion to spring length. In such cases the spring must be most carefully designed and precisely formed to guard against localized flexure with attendant risk of fatigue failure.

One mode of applying the invention defined is illustrated in the accompanying drawing in which Figure 1 i a view partly in side elevation and partly in axial section. showing the complete P p. I

Figure 2 is a'section on the line 22 of Figure 1.

Figure 3 is an enlarged view of the actuating heads '25, each of which carries a circular shoe plications and particularly details claimed in the second application above identified.

The pump body comprises two portions 6 and 1 which telescope together and confine a cylinder block 8 having nine cylinder forming bores which are spaced uniformly in a circle around a central bore which receives the drive shaft.

The pump plungers are generally indicated by the numeral 9 and the pump shaft is generally indicated by the numeral II. It is counterbored at its inner end (the right-hand end as viewed in Figure 1), and the counterbore communicates it will suffice to say that the counterbore com-- municates with ports, also not shown, in the swash plate It so that entering oil flows axially through the shaft and reaches the space IS within the portion 6 of the housing.

The discharge valves l6 seat against the righthand face of the cylinder block 8. They are urged closed by coil compression springs l1 and control fiow to a discharge chamber I! which is in communication with the discharge connection IS.

The flange 2| on the portion 6 of the pump housing is the mounting flange. The fitting 22 is merely a self-aligning floating connection for the drive shaft. These details are elaborated in the prior applications and certain of them are there claimed. They are significant here merely as in-' 9 has a head formed with an external flange 24.

The head is counterbored to afford a spherical recess into which are pressed spherical thrust 26 having a plane face which is in sliding engagement with the creep ring 23.

mechanism visible inFigure 1 designed to indi- Making a close but free slidingfit with each plunger 9 is a corresponding return thrust head 21 which is shouldered to serve as a spring seat. A short rather stiff coil compression spring 28 reacts between the flange on the .head of the plunger and the shoulder on the member 21, the

arrangement being such that the spring can never contact the plunger.

The inner or righthand face of each member 21 is a cone and the angle of the cone is: an ime D rtant detail of the invention.

Also mounted on the shaft ll close to the cylinderblock 8 is an opposed axial cam 29.. This is shown with a plane face which is not parallel with the plane face of the swash plate ll but makes a small dihedral angle therewith, such that when the shaft ll turns 180 the axial displacement of the thrust rim of the cam 29 'is the same as the axial displacement of theplunger 9 by the swash plate H.

The reason for the dihedral angle will be apparent when one considers that the effective radius of the cam 29 differs from the effective radius of the swash plate I. If the inclinations of the working faces of the cam and swash plate are so coordinated that they produce the same displacements of the plungers at their high and low points, they will produce the same displacements at all points. Any departure from absolute precision in manufacture is compensated by the springs 28. This is one of the functions of the springs but the springs are also useful in taking up the back-lash and in cushioning against shock.

The margin of the cam 29 is given a rounded configuration. The generating curve is an involute; Stated differently, any section of the rounded rim cut by a plane radial to the shaft II is an involute. The base circle for an appropriate involute is indicated by a legend in Figure 3. In that figure it will be observed that the contacting element of the cone on the upper one of the thrust members 21, if projected, would lie in the plane of the face of the cam 29. This relationship gives the minimum practicable obliquity of thrust, and hence is preferred.

The geometry of the rim configuration is identical with the geometry of the involute system of toothed gearing. See Schwamb and Merrill Elements of Mechanism," John Wiley and Sons, 1904, page 219 et seq. In the involute system the rack has straight teeth with their faces perpendicular to the line of obliquity. That is the reason for the use of a conical surface on the member 21. The result of using the involute configuration is the attainment of correct conjugate curves of simple form.

There is a very slight varyin error occasioned by the tilt of the cam. This error is zero at the contact points shown in Figure 3 and reaches its maximum at points displaced 90 of are therefrom around the perimeter of the cam 29. The error is microscopic and negligible.

From the construction described, it follows that as the shaft ll rotates the plungers 9 are reciprocated, while the members 21 have no motion relative to the plungers. The springs 28 are stiff enough to force the plungers to the left, that is outward against any suction resistance that may occur. From this it' will follow that within the limits of load imposed on the pump, the plungers are positively reciprocated. The springs 28' are not not worked but function merely to take up all back-lash and inhibit lost motion. For this reason the springs are not subject to fatigue failure. Nevertheless all the advantages of sprin thrust are retained.

The cone and involute are believed to be the In the claims the term conjugate curves" is used in the sense in which it is used in gear design. In this sense the term does not exclude a straight line which can be regarded as an arc of infinite radius. Since the collars do not move on their plungers as the shaft rotates, the springs operate under constant stress. Of course they must be mounted under initial stress sufficient to draw the plunger against the suction reaction at the maximum rotary speed for which the pump is designed.

The facts that the thrust shoes and the collars are each rotatable relatively to their plungers, and that the plungers also are rotatable, assures free action and distribution of wear.

While one embodiment of the invention has been described in considerable detail, this is merely illustrative of the best known embodiment and should be regarded as illustrative and not limiting. The scope of the invention will be defined in the claims.

What is claimed is:

1. The combination of a rotary shaft; a plunger guided to move in a path parallel with the axis of said shaft; a swash plate turning with the shaft and reacting against the end of the plunger to actuate it in one longitudinal direction; an abutment slidable on said plunger and projecting from the side thereof; a spring reacting between said plunger and abutment; and a cam on said shaft reactin on said abutment to actuate the plunger in the other longitudinal direction, the parts being so dimensioned that the spring is constantly under an approximately uniform stress.

2. The combination of a rotary shaft; a plunger guided to move in a path parallel with the axis of said shaft; a swash plate turning with the shaft and reacting against the end of the plunger to actuate it in one longitudinal direction; an abutment slidable on said plunger and projecting from the side thereof; a spring reacting between said plunger and abutment; and a cam on said shaft reacting on said abutment to actuate the plunger in the other longitudinal direction, the coacting portions of the cam and abutment conforming to conjugate curves and the parts being so dimensioned that the spring is constantly under an approximately uniform stress as the device operates.

'3. The combination of a rotary shaft; a rotatable plunger guided to reciprocate longitudinally in a path parallel with the axis of said shaft; a swash plate turning with said shaft and reacting against one end of the plunger to actuate it in one longitudinal direction; a collar slidable on said plunger; a spring surrounding the plunger and sustaining said collar; and a cam on said shaft reacting at its margin on said collar to actuate the plunger in the other longitudinal direction, the margin of the cam and the coacting face of the collar conforming to conjugate curves and the parts being so dimensioned that the spring is constantly under approximately uniform stress.

4. The combination defined in claim 3 in which the coacting surfaces on the collar and cam are respectively a right cone and an involute fillet.

5. The combination defined in claim 3 in which each plunger has a rotatable and'universally tiltable thrust'shoe engaging the swash plate, and the collar is rotatable on the plunger.

MATTHEW W. HUBER. 

